<!DOCTYPE html>
<style>
@keyframes test {
  from { background-position: 0 0;}
  to { background-position: 1px 1px;}
}
div {
  position: absolute;
  top: 4em;
  width: 400px;
}
.animated {
  position: absolute;
  animation: test 1000s;
}
</style>

<div>
  <span>This sentence shoul</span>
  <span class="animated">d span a single line.</span>
</div>
